1NCAT(1)                      Ncat Reference Guide                      NCAT(1)
2
3
4

NAME

6       ncat - Concatenate and redirect sockets
7

SYNOPSIS

9       ncat [OPTIONS...] [hostname] [port]
10

DESCRIPTION

12       Ncat is a feature-packed networking utility which reads and writes data
13       across networks from the command line. Ncat was written for the Nmap
14       Project and is the culmination of the currently splintered family of
15       Netcat incarnations. It is designed to be a reliable back-end tool to
16       instantly provide network connectivity to other applications and users.
17       Ncat will not only work with IPv4 and IPv6 but provides the user with a
18       virtually limitless number of potential uses.
19
20       Among Ncat's vast number of features there is the ability to chain
21       Ncats together; redirection of TCP, UDP, and SCTP ports to other sites;
22       SSL support; and proxy connections via SOCKS4, SOCKS5 or HTTP proxies
23       (with optional proxy authentication as well). Some general principles
24       apply to most applications and thus give you the capability of
25       instantly adding networking support to software that would normally
26       never support it.
27

OPTIONS SUMMARY

29           Ncat 7.93 ( https://nmap.org/ncat )
30           Usage: ncat [options] [hostname] [port]
31
32           Options taking a time assume seconds. Append 'ms' for milliseconds,
33           's' for seconds, 'm' for minutes, or 'h' for hours (e.g. 500ms).
34             -4                         Use IPv4 only
35             -6                         Use IPv6 only
36             -U, --unixsock             Use Unix domain sockets only
37                 --vsock                Use vsock sockets only
38             -C, --crlf                 Use CRLF for EOL sequence
39             -c, --sh-exec <command>    Executes the given command via /bin/sh
40             -e, --exec <command>       Executes the given command
41                 --lua-exec <filename>  Executes the given Lua script
42             -g hop1[,hop2,...]         Loose source routing hop points (8 max)
43             -G <n>                     Loose source routing hop pointer (4, 8, 12, ...)
44             -m, --max-conns <n>        Maximum <n> simultaneous connections
45             -h, --help                 Display this help screen
46             -d, --delay <time>         Wait between read/writes
47             -o, --output <filename>    Dump session data to a file
48             -x, --hex-dump <filename>  Dump session data as hex to a file
49             -i, --idle-timeout <time>  Idle read/write timeout
50             -p, --source-port port     Specify source port to use
51             -s, --source addr          Specify source address to use (doesn't affect -l)
52             -l, --listen               Bind and listen for incoming connections
53             -k, --keep-open            Accept multiple connections in listen mode
54             -n, --nodns                Do not resolve hostnames via DNS
55             -t, --telnet               Answer Telnet negotiations
56             -u, --udp                  Use UDP instead of default TCP
57                 --sctp                 Use SCTP instead of default TCP
58             -v, --verbose              Set verbosity level (can be used several times)
59             -w, --wait <time>          Connect timeout
60             -z                         Zero-I/O mode, report connection status only
61                 --append-output        Append rather than clobber specified output files
62                 --send-only            Only send data, ignoring received; quit on EOF
63                 --recv-only            Only receive data, never send anything
64                 --no-shutdown          Continue half-duplex when receiving EOF on stdin
65                 --allow                Allow only given hosts to connect to Ncat
66                 --allowfile            A file of hosts allowed to connect to Ncat
67                 --deny                 Deny given hosts from connecting to Ncat
68                 --denyfile             A file of hosts denied from connecting to Ncat
69                 --broker               Enable Ncat's connection brokering mode
70                 --chat                 Start a simple Ncat chat server
71                 --proxy <addr[:port]>  Specify address of host to proxy through
72                 --proxy-type <type>    Specify proxy type ("http", "socks4", "socks5")
73                 --proxy-auth <auth>    Authenticate with HTTP or SOCKS proxy server
74                 --proxy-dns <type>     Specify where to resolve proxy destination
75                 --ssl                  Connect or listen with SSL
76                 --ssl-cert             Specify SSL certificate file (PEM) for listening
77                 --ssl-key              Specify SSL private key (PEM) for listening
78                 --ssl-verify           Verify trust and domain name of certificates
79                 --ssl-trustfile        PEM file containing trusted SSL certificates
80                 --ssl-ciphers          Cipherlist containing SSL ciphers to use
81                 --ssl-servername       Request distinct server name (SNI)
82                 --ssl-alpn             ALPN protocol list to use
83                 --version              Display Ncat's version information and exit
84
85           See the ncat(1) manpage for full options, descriptions and usage examples
86
87

CONNECT MODE AND LISTEN MODE

89       Ncat operates in one of two primary modes: connect mode and listen
90       mode. Other modes, such as the HTTP proxy server, act as special cases
91       of these two. In connect mode, Ncat works as a client. In listen mode
92       it is a server.
93
94       In connect mode, the hostname and port arguments tell what to connect
95       to.  hostname is required, and may be a hostname or IP address. If port
96       is supplied, it must be a decimal port number. If omitted, it defaults
97       to 31337.
98
99       In listen mode, hostname and port control the address the server will
100       bind to. Both arguments are optional in listen mode. If hostname is
101       omitted, it defaults to listening on all available addresses over IPv4
102       and IPv6. If port is omitted, it defaults to 31337.
103

PROTOCOL OPTIONS

105       -4 (IPv4 only)
106           Force the use of IPv4 only.
107
108       -6 (IPv6 only)
109           Force the use of IPv6 only.
110
111       -U, --unixsock (Use Unix domain sockets)
112           Use Unix domain sockets rather than network sockets. This option
113           may be used on its own for stream sockets, or combined with --udp
114           for datagram sockets. A description of -U mode is in the section
115           called “UNIX DOMAIN SOCKETS”.
116
117       -u, --udp (Use UDP)
118           Use UDP for the connection (the default is TCP).
119
120       --sctp (Use SCTP)
121           Use SCTP for the connection (the default is TCP). SCTP support is
122           implemented in TCP-compatible mode.
123
124       --vsock (Use AF_VSOCK sockets)
125           Use AF_VSOCK sockets rather than the default TCP sockets (Linux
126           only). This option may be used on its own for stream sockets or
127           combined with --udp for datagram sockets. A description of --vsock
128           mode is in the section called “AF_VSOCK SOCKETS”.
129

CONNECT MODE OPTIONS

131       -g hop1[,hop2,...] (Loose source routing)
132           Sets hops for IPv4 loose source routing. You can use -g once with a
133           comma-separated list of hops, use -g multiple times with single
134           hops to build the list, or combine the two. Hops can be given as IP
135           addresses or hostnames.
136
137       -G ptr (Set source routing pointer)
138           Sets the IPv4 source route “pointer” for use with -g. The argument
139           must be a multiple of 4 and no more than 28. Not all operating
140           systems support setting this pointer to anything other than four.
141
142       -p port, --source-port port (Specify source port)
143           Set the port number for Ncat to bind to.
144
145       -s host, --source host (Specify source address)
146           Set the address for Ncat to bind to.
147

LISTEN MODE OPTIONS

149       See the section called “ACCESS CONTROL OPTIONS” for information on
150       limiting the hosts that may connect to the listening Ncat process.
151
152       -l, --listen (Listen for connections)
153           Listen for connections rather than connecting to a remote machine
154
155       -m numconns, --max-conns numconns (Specify maximum number of
156       connections)
157           The maximum number of simultaneous connections accepted by an Ncat
158           instance. 100 is the default (60 on Windows).
159
160       -k, --keep-open (Accept multiple connections)
161           Normally a listening server accepts only one connection and then
162           quits when the connection is closed. This option makes it accept
163           multiple simultaneous connections and wait for more connections
164           after they have all been closed. It must be combined with --listen.
165           In this mode there is no way for Ncat to know when its network
166           input is finished, so it will keep running until interrupted. This
167           also means that it will never close its output stream, so any
168           program reading from Ncat and looking for end-of-file will also
169           hang.
170
171       --broker (Connection brokering)
172           Allow multiple parties to connect to a centralised Ncat server and
173           communicate with each other. Ncat can broker communication between
174           systems that are behind a NAT or otherwise unable to directly
175           connect. This option is used in conjunction with --listen, which
176           causes the --listen port to have broker mode enabled.
177
178       --chat (Ad-hoc “chat server”)
179           The --chat option enables chat mode, intended for the exchange of
180           text between several users. In chat mode, connection brokering is
181           turned on. Ncat prefixes each message received with an ID before
182           relaying it to the other connections. The ID is unique for each
183           connected client. This helps distinguish who sent what.
184           Additionally, non-printing characters such as control characters
185           are escaped to keep them from doing damage to a terminal.
186

SSL OPTIONS

188       --ssl (Use SSL)
189           In connect mode, this option transparently negotiates an SSL
190           session with an SSL server to securely encrypt the connection. This
191           is particularly handy for talking to SSL enabled HTTP servers, etc.
192
193           In server mode, this option listens for incoming SSL connections,
194           rather than plain untunneled traffic.
195
196           In UDP connect mode, this option enables Datagram TLS (DTLS). This
197           is not supported in server mode.
198
199       --ssl-verify (Verify server certificates)
200           In client mode, --ssl-verify is like --ssl except that it also
201           requires verification of the server certificate. Ncat comes with a
202           default set of trusted certificates in the file ca-bundle.crt.
203           Some operating systems provide a default list of trusted
204           certificates; these will also be used if available. Use
205           --ssl-trustfile to give a custom list. Use -v one or more times to
206           get details about verification failures.  Ncat does not check for
207           revoked certificates.
208
209           This option has no effect in server mode.
210
211       --ssl-cert certfile.pem (Specify SSL certificate)
212           This option gives the location of a PEM-encoded certificate files
213           used to authenticate the server (in listen mode) or the client (in
214           connect mode). Use it in combination with --ssl-key.
215
216       --ssl-key keyfile.pem (Specify SSL private key)
217           This option gives the location of the PEM-encoded private key file
218           that goes with the certificate named with --ssl-cert.
219
220       --ssl-trustfile cert.pem (List trusted certificates)
221           This option sets a list of certificates that are trusted for
222           purposes of certificate verification. It has no effect unless
223           combined with --ssl-verify. The argument to this option is the name
224           of a PEM file containing trusted certificates. Typically, the file
225           will contain certificates of certification authorities, though it
226           may also contain server certificates directly. When this option is
227           used, Ncat does not use its default certificates.
228
229       --ssl-ciphers cipherlist (Specify SSL ciphersuites)
230           This option sets the list of ciphersuites that Ncat will use when
231           connecting to servers or when accepting SSL connections from
232           clients. The syntax is described in the OpenSSL ciphers(1) man
233           page, and defaults to
234           ALL:!aNULL:!eNULL:!LOW:!EXP:!RC4:!MD5:@STRENGTH
235
236       --ssl-servername name (Request distinct server name)
237           In client mode, this option sets the TLS SNI (Server Name
238           Indication) extension, which tells the server the name of the
239           logical server Ncat is contacting. This is important when the
240           target server hosts multiple virtual servers at a single underlying
241           network address. If the option is not provided, the TLS SNI
242           extension will be populated with the target server hostname.
243
244       --ssl-alpn ALPN list (Specify ALPN protocol list)
245           This option allows you to specify a comma-separated list of
246           protocols to send via the Application-Layer Protocol Negotiation
247           (ALPN) TLS extension. Not supported by all versions of OpenSSL.
248

PROXY OPTIONS

250       --proxy host[:port] (Specify proxy address)
251           Requests proxying through host:port, using the protocol specified
252           by --proxy-type.
253
254           If no port is specified, the proxy protocol's well-known port is
255           used (1080 for SOCKS and 3128 for HTTP). When specifying an IPv6
256           HTTP proxy server using the IP address rather than the hostname,
257           the square-bracket notation (for example [2001:db8::1]:8080) MUST
258           be used to separate the port from the IPv6 address. If the proxy
259           requires authentication, use --proxy-auth.
260
261       --proxy-type proto (Specify proxy protocol)
262           In connect mode, this option requests the protocol proto to connect
263           through the proxy host specified by --proxy. In listen mode, this
264           option has Ncat act as a proxy server using the specified protocol.
265
266           The currently available protocols in connect mode are http
267           (CONNECT), socks4 (SOCKSv4), and socks5 (SOCKSv5). The only server
268           currently supported is http. If this option is not used, the
269           default protocol is http.
270
271       --proxy-auth user[:pass] (Specify proxy credentials)
272           In connect mode, gives the credentials that will be used to connect
273           to the proxy server. In listen mode, gives the credentials that
274           will be required of connecting clients. For use with --proxy-type
275           http or --proxy-type socks5, the form should be username:password.
276           For --proxy-type socks4, it should be a username only.
277
278           These credentials can be alternatively passed onto Ncat by setting
279           environment variable NCAT_PROXY_AUTH, which reduces the risk of the
280           credentials being captured in process logs. (Option --proxy-auth
281           takes precedence.)
282
283       --proxy-dns type (Specify where to resolve proxy destination)
284           In connect mode, it provides control over whether proxy destination
285           hostnames are resolved by the remote proxy server or locally, by
286           Ncat itself. Possible values for type are:
287
288           local - Hostnames are resolved locally on the Ncat host. Ncat exits
289           with error if the hostname cannot be resolved.
290
291           remote - Hostnames are passed directly onto the remote proxy
292           server. This is the default behavior.
293
294           both - Hostname resolution is first attempted on the Ncat host.
295           Unresolvable hostnames are passed onto the remote proxy server.
296
297           none - Hostname resolution is completely disabled. Only a literal
298           IPv4 or IPv6 address can be used as the proxy destination.
299
300           Local hostname resolution generally respects IP version specified
301           with options -4 or -6, except for SOCKS4, which is incompatible
302           with IPv6.
303

COMMAND EXECUTION OPTIONS

305       -e command, --exec command (Execute command)
306           Execute the specified command after a connection has been
307           established. The command must be specified as a full pathname. All
308           input from the remote client will be sent to the application and
309           responses sent back to the remote client over the socket, thus
310           making your command-line application interactive over a socket.
311           Combined with --keep-open, Ncat will handle multiple simultaneous
312           connections to your specified port/application like inetd. Ncat
313           will only accept a maximum, definable, number of simultaneous
314           connections controlled by the -m option. By default this is set to
315           100 (60 on Windows).
316
317       -c command, --sh-exec command (Execute command via sh)
318           Same as -e, except it tries to execute the command via /bin/sh.
319           This means you don't have to specify the full path for the command,
320           and shell facilities like environment variables are available.
321
322       --lua-exec file (Execute a .lua script)
323           Runs the specified file as a Lua script after a connection has been
324           established, using a built-in interpreter. Both the script's
325           standard input and the standard output are redirected to the
326           connection data streams.
327
328       All exec options add the following variables to the child's
329       environment:
330
331       NCAT_REMOTE_ADDR, NCAT_REMOTE_PORT
332           The IP address and port number of the remote host. In connect mode,
333           it's the target's address; in listen mode, it's the client's
334           address.
335
336       NCAT_LOCAL_ADDR, NCAT_LOCAL_PORT
337           The IP address and port number of the local end of the connection.
338
339       NCAT_PROTO
340           The protocol in use: one of TCP, UDP, and SCTP.
341

ACCESS CONTROL OPTIONS

343       --allow host[,host,...] (Allow connections)
344           The list of hosts specified will be the only hosts allowed to
345           connect to the Ncat process. All other connection attempts will be
346           disconnected. In case of a conflict between --allow and --deny,
347           --allow takes precedence. Host specifications follow the same
348           syntax used by Nmap.
349
350       --allowfile file (Allow connections from file)
351           This has the same functionality as --allow, except that the allowed
352           hosts are provided in a new-line delimited allow file, rather than
353           directly on the command line.
354
355       --deny host[,host,...] (Deny connections)
356           Issue Ncat with a list of hosts that will not be allowed to connect
357           to the listening Ncat process. Specified hosts will have their
358           session silently terminated if they try to connect. In case of a
359           conflict between --allow and --deny, --allow takes precedence. Host
360           specifications follow the same syntax used by Nmap.
361
362       --denyfile file (Deny connections from file)
363           This is the same functionality as --deny, except that excluded
364           hosts are provided in a new-line delimited deny file, rather than
365           directly on the command line.
366

TIMING OPTIONS

368       These options accept a time parameter. This is specified in seconds by
369       default, though you can append ms, s, m, or h to the value to specify
370       milliseconds, seconds, minutes, or hours.
371
372       -d time, --delay time (Specify line delay)
373           Set the delay interval for lines sent. This effectively limits the
374           number of lines that Ncat will send in the specified period. This
375           may be useful for low-bandwidth sites, or have other uses such as
376           coping with annoying iptables --limit options.
377
378       -i time, --idle-timeout time (Specify idle timeout)
379           Set a fixed timeout for idle connections. If the idle timeout is
380           reached, the connection is terminated.
381
382       -w time, --wait time (Specify connect timeout)
383           Set a fixed timeout for connection attempts.
384

OUTPUT OPTIONS

386       -o file, --output file (Save session data)
387           Dump session data to a file
388
389       -x file, --hex-dump file (Save session data in hex)
390           Dump session data in hex to a file.
391
392       --append-output (Append output)
393           Issue Ncat with --append-ouput along with -o and/or -x and it will
394           append the resulted output rather than truncating the specified
395           output files.
396
397       -v, --verbose (Be verbose)
398           Issue Ncat with -v and it will be verbose and display all kinds of
399           useful connection based information. Use more than once (-vv,
400           -vvv...) for greater verbosity.
401

MISC OPTIONS

403       -C, --crlf (Use CRLF as EOL)
404           This option tells Ncat to convert LF line endings to CRLF when
405           taking input from standard input.  This is useful for talking to
406           some stringent servers directly from a terminal in one of the many
407           common plain-text protocols that use CRLF for end-of-line.
408
409       -h, --help (Help screen)
410           Displays a short help screen with common options and parameters,
411           and then exits.
412
413       --recv-only (Only receive data)
414           If this option is passed, Ncat will only receive data and will not
415           try to send anything.
416
417       --send-only (Only send data)
418           If this option is passed, then Ncat will only send data and will
419           ignore anything received. This option also causes Ncat to close the
420           network connection and terminate after EOF is received on standard
421           input.
422
423       --no-shutdown (Do not shutdown into half-duplex mode)
424           If this option is passed, Ncat will not invoke shutdown on a socket
425           after seeing EOF on stdin. This is provided for
426           backward-compatibility with OpenBSD netcat, which exhibits this
427           behavior when executed with its '-d' option.
428
429       -n, --nodns (Do not resolve hostnames)
430           Completely disable hostname resolution across all Ncat options,
431           such as the destination, source address, source routing hops, and
432           the proxy. All addresses must be specified numerically. (Note that
433           resolution of proxy destinations is controlled separately via
434           option --proxy-dns.)
435
436       -t, --telnet (Answer Telnet negotiations)
437           Handle DO/DONT WILL/WONT Telnet negotiations. This makes it
438           possible to script Telnet sessions with Ncat.
439
440       --version (Display version)
441           Displays the Ncat version number and exits.
442

UNIX DOMAIN SOCKETS

444       The -U option (same as --unixsock) causes Ncat to use Unix domain
445       sockets rather than network sockets. Unix domain sockets exist as an
446       entry in the filesystem. You must give the name of a socket to connect
447       to or to listen on. For example, to make a connection,
448
449       ncat -U ~/unixsock
450
451       To listen on a socket:
452
453       ncat -l -U ~/unixsock
454
455       Listen mode will create the socket if it doesn't exist. The socket will
456       continue to exist after the program ends.
457
458       Both stream and datagram domain sockets are supported. Use -U on its
459       own for stream sockets, or combine it with --udp for datagram sockets.
460       Datagram sockets require a source socket to connect from. By default, a
461       source socket with a random filename will be created as needed, and
462       deleted when the program ends. Use the --source with a path to use a
463       source socket with a specific name.
464

AF_VSOCK SOCKETS

466       The --vsock option causes Ncat to use AF_VSOCK sockets rather than
467       network sockets. A CID must be given instead of a hostname or IP
468       address. For example, to make a connection to the host,
469
470       ncat --vsock 2 1234
471
472       To listen on a socket:
473
474       ncat -l --vsock 1234
475
476       Both stream and datagram domain sockets are supported, but socket type
477       availability depends on the hypervisor. Use --vsock on its own for
478       stream sockets, or combine it with --udp for datagram sockets.
479

EXAMPLES

481       Connect to example.org on TCP port 8080.
482           ncat example.org 8080
483
484       Listen for connections on TCP port 8080.
485           ncat -l 8080
486
487       Redirect TCP port 8080 on the local machine to host on port 80.
488           ncat --sh-exec "ncat example.org 80" -l 8080 --keep-open
489
490       Bind to TCP port 8081 and attach /bin/bash for the world to access
491       freely.
492           ncat --exec "/bin/bash" -l 8081 --keep-open
493
494       Bind a shell to TCP port 8081, limit access to hosts on a local
495       network, and limit the maximum number of simultaneous connections to 3.
496           ncat --exec "/bin/bash" --max-conns 3 --allow 192.168.0.0/24 -l
497           8081 --keep-open
498
499       Connect to smtphost:25 through a SOCKS4 server on port 1080.
500           ncat --proxy socks4host --proxy-type socks4 --proxy-auth joe
501           smtphost 25
502
503       Connect to smtphost:25 through a SOCKS5 server on port 1080.
504           ncat --proxy socks5host --proxy-type socks5 --proxy-auth joe:secret
505           smtphost 25
506
507       Create an HTTP proxy server on localhost port 8888.
508           ncat -l --proxy-type http localhost 8888
509
510       Send a file over TCP port 9899 from host2 (client) to host1 (server).
511           HOST1$ ncat -l 9899 > outputfile
512
513           HOST2$ ncat HOST1 9899 < inputfile
514
515       Transfer in the other direction, turning Ncat into a “one file” server.
516           HOST1$ ncat -l 9899 < inputfile
517
518           HOST2$ ncat HOST1 9899 > outputfile
519

EXIT CODE

521       The exit code reflects whether a connection was made and completed
522       successfully. 0 means there was no error. 1 means there was a network
523       error of some kind, for example “Connection refused” or “Connection
524       reset”. 2 is reserved for all other errors, like an invalid option or a
525       nonexistent file.
526

BUGS

528       Like its authors, Ncat isn't perfect. But you can help make it better
529       by sending bug reports or even writing patches. If Ncat doesn't behave
530       the way you expect, first upgrade to the latest version available from
531       https://nmap.org. If the problem persists, do some research to
532       determine whether it has already been discovered and addressed. Try
533       Googling the error message or browsing the nmap-dev archives at
534       https://seclists.org/.
535
536       Read this full manual page as well. If nothing comes of this, mail a
537       bug report to <dev@nmap.org>. Please include everything you have
538       learned about the problem, as well as what version of Ncat you are
539       running and what operating system version it is running on. Problem
540       reports and Ncat usage questions sent to dev@nmap.org are far more
541       likely to be answered than those sent to Fyodor directly.
542
543       Code patches to fix bugs are even better than bug reports. Basic
544       instructions for creating patch files with your changes are available
545       at https://svn.nmap.org/nmap/HACKING. Patches may be sent to nmap-dev
546       (recommended) or to Fyodor directly.
547

AUTHORS

549       •   Chris Gibson <chris@linuxops.net>
550
551       •   Gordon Lyon (Fyodor)<fyodor@nmap.org> (http://insecure.org)
552
553       •   Kris Katterjohn <katterjohn@gmail.com>
554
555       •   Mixter <mixter@gmail.com>
556
557       The original Netcat was written by *Hobbit* <hobbit@avian.org>. While
558       Ncat isn't built on any code from the “traditional” Netcat (or any
559       other implementation), Ncat is most definitely based on Netcat in
560       spirit and functionality.
561
563   Ncat Copyright and Licensing
564       Ncat is (C) 2005–2022 Nmap Software LLC. It is distributed as free and
565       open source software under the same license terms as our Nmap software.
566       Precise terms and further details are available from
567       https://nmap.org/man/man-legal.html.
568
569   Creative Commons License for this Ncat Guide
570       This Ncat Reference Guide is (C) 2005–2022 Nmap Software LLC. It is
571       hereby placed under version 3.0 of the Creative Commons Attribution
572       License[1]. This allows you redistribute and modify the work as you
573       desire, as long as you credit the original source. Alternatively, you
574       may choose to treat this document as falling under the same license as
575       Ncat itself (discussed previously).
576
577   Source Code Availability and Community Contributions
578       Source is provided to this software because we believe users have a
579       right to know exactly what a program is going to do before they run it.
580       This also allows you to audit the software for security holes (none
581       have been found so far).
582
583       Source code also allows you to port Nmap (which includes Ncat) to new
584       platforms, fix bugs, and add new features. You are highly encouraged to
585       send your changes to <dev@nmap.org> for possible incorporation into the
586       main distribution. By sending these changes to Fyodor or one of the
587       Insecure.Org development mailing lists, it is assumed that you are
588       offering the Nmap Project (Nmap Software LLC) the unlimited,
589       non-exclusive right to reuse, modify, and relicense the code. Nmap will
590       always be available open source, but this is important because the
591       inability to relicense code has caused devastating problems for other
592       Free Software projects (such as KDE and NASM). We also occasionally
593       relicense the code to third parties as discussed in the Nmap man page.
594       If you wish to specify special license conditions of your
595       contributions, just say so when you send them.
596
597   No Warranty
598       This program is distributed in the hope that it will be useful, but
599       WITHOUT ANY WARRANTY; without even the implied warranty of
600       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the Nmap
601       Public Source License for more details at https://nmap.org/npsl/, or in
602       the LICENSE file included with Nmap.
603
604   Inappropriate Usage
605       Ncat should never be installed with special privileges (e.g. suid
606       root).  That would open up a major security vulnerability as other
607       users on the system (or attackers) could use it for privilege
608       escalation.
609
610   Third-Party Software
611       This product includes software developed by the Apache Software
612       Foundation[2]. A modified version of the Libpcap portable packet
613       capture library[3] is distributed along with Ncat. The Windows version
614       of Ncat utilized the Libpcap-derived Npcap library[4] instead. Certain
615       raw networking functions use the Libdnet[5] networking library, which
616       was written by Dug Song.  A modified version is distributed with Ncat.
617       Ncat can optionally link with the OpenSSL cryptography toolkit[6] for
618       SSL version detection support. All of the third-party software
619       described in this paragraph is freely redistributable under BSD-style
620       software licenses.
621

NOTES

623        1. Creative Commons Attribution License
624           http://creativecommons.org/licenses/by/3.0/
625
626        2. Apache Software Foundation
627           http://www.apache.org
628
629        3. Libpcap portable packet capture library
630           http://www.tcpdump.org
631
632        4. Npcap library
633           https://npcap.com
634
635        5. Libdnet
636           http://libdnet.sourceforge.net
637
638        6. OpenSSL cryptography toolkit
639           http://www.openssl.org
640
641
642
643Ncat                              08/31/2022                           NCAT(1)
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